DNA is used to match a sample retrieved from a crime scene with DNA retrieved from a suspect to identify a connection of the suspect to the crime scene. Current DNA analyses do not permit identifying the source of DNA from a suspect. However, certain forensic cases, such as sexual abuse require confirmation that a DNA from a suspect is from an intimate body fluid.
Techniques currently used for body fluid identification are not based on DNA analysis. For example, microscopic observation of sperms is used to identify semen as a source body fluid or histological staining of glycogen-rich cells is used to identify vaginal cells. However, these tests are not reliable. For example, if the male donor does not produce sperm, the source cannot be identified as semen. Similarly, false negatives can occur because the glycogen content of vaginal cells varies depending on the menstrual cycle and reproductive age; whereas, false positives can occur because buccal and urogenital skin cells (even from males) can have high glycogen.
Certain other methods are based on protein/enzyme reactivity or cell staining and are merely presumptive. These methods may have low sensitivity and render the portion of the sample useless for subsequent analysis. Therefore, forensic laboratories may be left to choose between isolating DNA to compare a suspect's DNA or determining body fluid of origin.
Certain other methods of identifying source body fluid are based on analyzing RNA transcripts. However, the need to identify a body fluid often arises after DNA is isolated. To perform an RNA transcript analysis, the laboratory technician would have to retrieve a new portion of the original sample (if available) and isolate RNA. However, the original sample may have already been consumed.